1. Field of the Invention
This invention relates to a transmission apparatus for a vehicle and, more specifically, to a compact transmission which is advantageous especially in a front-engine, front-drive motorcar where the size of the transmission is largely restricted with relation to the space available.
2. Description of the Prior Art
There has been hitherto described in Japanese Patent Unexamined Publication Sho No. 54-103958 and Japanese Patent Unexamined Publication Sho No. 55-51160, a transmission for a front-drive motorcar having three forward speeds and reverse. An input shaft and an output shaft are provided in parallel one with another in a transmission casing and are supported rotatably on a front wall and a middle wall of the casing. A first-speed driving train for a low speed is provided positioned to the rear of the middle wall. A second-speed driving train for a middle speed is provided at a middle position. A third-speed driving train for a high speed is provided on a front side on the second-speed driving train and a reverse driving train is provided on a rear side thereof. The second-speed, third-speed and reverse driving trains are disposed between the middle wall and the front wall of the casing.
This type of apparatus is advantageous in that the shafts can be made small in diameter because the first-speed driving train and the reverse driving train, which have a large bending force acting on the shafts, are disposed near the middle wall and in front and rear thereof.
Additionally, this type of apparatus is arranged so that the second-speed clutch for the second-speed driving train provided on the input shaft may be used also for a clutch for the reverse driving train. The reverse driving gear for the reverse driving train is integrally connected to the second-speed driving gear on the output side of the second-speed clutch. The second-speed driven gear and a reverse driven gear which are meshed with the respective driving gears are arranged to be selectively engaged with the output shaft through a selection mechanism provided between the two driven gears. In this manner, a clutch to be exclusively used for driving in reverse is omitted so that the axial dimension of the transmission apparatus can be shortened by that extent.
It is possible in this arrangement to add a fourth-speed driving train in order to increase the number of speed stages. However, if the fourth-speed driving train is simply added thereto, the axial size or dimension of the apparatus becomes too long.
Further, the simple addition of a fourth-speed driving train to the above-known apparatus would generate certain further problems. When the vehicle is being driven forward in the fourth or highest driving speed, the second-speed driven gear is connected by the selection mechanism to the output shaft. Since the second-speed driving gear is always meshed with the second-speed driven gear, the second-speed driving gear is also rotated. Since the normal gear ratio between the second-speed driving gear and the second-speed driven gear is a reduction ratio, that is, the driven gear moves at a rotational speed slower than the driving gear, at the time of high speed rotation of the output shaft by the fourth-speed driving train, the second-speed driven gear rotates the second-speed driving gear at a higher rotational speed than that of the output shaft. Since the reverse driving gear is integral with the second speed driving gear, the reverse driving train including an idler gear between the driving gear and the driven gear is given a high speed rotation. This generates a large amount of gear noise by the various engaged gears at the time of high speed rotation thereof by the fourth speed driving train. Additionally, when these gears are meshed in lubricating oil, a large power loss results caused by the resistance to agitation by the lubricating oil.